1. Field of the Invention
This invention is directed to a stabilized denture paste or cream and to a method for cleaning dentures using a stabilized denture paste.
2. Description of Related Art
Dentures and other removable full or partial dental prostheses, like the teeth they replace, require regular cleaning to maintain the oral health of the wearer. The considerations that go into designing cleaning compositions for such dental prostheses, however, differ from considerations in designing cleaning compositions for teeth.
Teeth are generally cleaned either by brushing with a dentifrice (or tooth powder) or by rinsing the mouth with a mouthwash. Dentifrices may contain cleansing ingredients, detergents and abrasives. Mouthwashes may contain alcohol or other agents to kill germs in the mouth. An important consideration in formulating a dentifrice or mouthwash, however, is the organoleptic quality of the finished formulation. Another important consideration is the strength of the ingredients used. If the ingredients are too weak, the dentifrice or mouthwash will not clean properly. If the ingredients are too strong, the dentifrice or mouthwash could damage the soft tissues in the mouth.
Dentifrices and mouthwashes may contain other ingredients to strengthen teeth, such as fluorides, hypersensitivity treatments, such as potassium nitrate, or remineralization ingredients, such as hydroxyapatite.
Dental prostheses are typically cleaned either through immersion in a bath containing a cleansing agent or by brushing with a specially formulated cream. Immersion has the advantage of offering complete cleaning, because brushing can miss hard to reach areas of the dental prosthesis. Brushing, however, offers the advantage of both mechanical cleaning and chemical cleaning, and many people prefer brushing with a paste to ensure thorough cleaning of the prosthesis.
Dentures and dental prostheses, however, are not natural teeth. Modern dental prostheses are usually made from polymeric materials. These materials can withstand a high level of cleaning activity, and prostheses do not require any of the special ingredients, such as hypersensitivity ingredients, remineralization ingredients and fluoride treatments, found in dentifrices.
Because of the differing design parameters for denture pastes and dentifrices, many considerations affecting dentifrice formulations are not pertinent for denture pastes.
For example, U.S. Pat. No. 5,372,802 discloses a dentifrice that includes a peroxyacid compound such as hydrogen peroxide, a fluoride-containing anticaries agent and a zinc compound such as zinc citrate. The zinc compound inhibits decomposition that ordinarily would be induced by the presence of fluoride. A denture paste does not need fluoride, since the acrylic polymer of many dental prostheses is not strengthened by fluoride.
Despite the general absence of a need for fluoride in treating dentures and dental prostheses, U.S. Pat. No. 5,736,158 to Quast, issued Apr. 7, 1998, teaches a denture cleanser tablet or paste for partial dental prostheses (that do not replace all teeth in the mouth) containing high levels of fluoride. This fluoride may be sodium fluoride or sodium monofluorophosphate and may be combined with a peroxyacid cleansing agent such as calcium peroxide in a two-layer denture tablet. The fluoride is present at a high level to impregnate the dental prosthesis during cleaning and to leach out during use, thereby providing a fluoride treatment for adjacent natural teeth.
A recent development in dentifrices has been the development of baking soda and peroxide dentifrices. These dentifrices have been formulated in "split tube" designs to prevent reactions between peroxide and baking soda during storage. One example of a split tube dentifrice is found in U.S. Pat. No. 5,599,525 to Hsu et al., issued Feb. 4, 1997. This patent is directed to a split tube configuration having, among other ingredients, calcium peroxide, sodium bicarbonate and a fluoride source such as sodium monofluorophosphate.
Many attempts Wave been made to stabilize the baking soda and peroxide in a single tube configuration. U.S. Pat. No. 4,837,008, for example, discloses an aqueous dentifrice containing a peroxide and/or bicarbonate ingredient. The ingredients are coated to prevent reaction during storage. A disadvantage to such a dentifrice is that release of the ingredients for cleaning effect during use is diminished by the presence of the barrier coating.
Another approach has been stabilizing the formulation by adopting a substantially anhydrous system. U.S. Pat. No. 4,897,258 discloses an anhydrous dentifrice containing calcium peroxide and sodium bicarbonate. The anhydrous state of the dentifrice prevents reaction between the ingredients. A disadvantage to such a dentifrice is that in spite of the anhydrous state of the dentifrice, limited storage ability is experienced. Anhydrous systems might also lead to poor dispersion of the ingredients in the dentifrice itself, and the formulation is expensive compared to water-based dentifrices. U.S. Pat. No. 4,971,782 discloses an anhydrous dentifrice containing peroxide and bicarbonate. One ingredient is coated with a water soluble coating and a peroxide stabilizer is included in the dentifrice to further enhance storage stability. In spite of the presence of the stabilizer, the dentifrice remains deficient in storage stability required for commercial use.
Attempts to stabilize the ingredients in a water-based dentifrice include those discussed in U.S. Pat. No. 5,565,190 to Santalucia et al., issued Oct. 15, 1996, and its divisional patent, U.S. Pat. No. 5,683,680 to Santalucia et al., issued Nov. 4, 1997. These patents disclose sodium hydroxide or sodium carbonate to stabilize a dentifrice composition containing peroxide and bicarbonate. U.S. Pat. No. 5,614,174 to Hsu et al., issued Mar. 25, 1997, is directed to a dentifrice comprising a peroxide, such as calcium peroxide, and sodium bicarbonate. The dentifrice may contain a fluoride source, such as sodium fluoride or sodium monofluorophosphate and the dentifrice is stabilized by the addition of polyethylene glycol 2000.
Other dentifrices have not recognized the problem. U.S. Pat. No. 4,603,045 to Smigel, issued Jul. 29, 1986, for example, is directed to a toothpaste adapted for cleaning natural teeth and bonded composite filling material. The toothpaste contains dicalcium phosphate, calcium carbonate, magnesium carbonate, sorbitol, corn starch, cellulose gum, calcium peroxide, sodium perborate, sodium lauryl sulfoacetate, aluminum hydroxide, saccharinate, flavoring, alkylparaben, sodium monofluoride phosphate, titanium dioxide and water. These ingredients must be present in a carefully balanced combination to achieve the objects of the patent.
U.S. Pat. No. 4,925,655 to Smigel et al., issued May 15, 1990, is directed to a powder composition soluble in water to form a mouthwash. The powder contains calcium peroxide, sodium perborate, sodium bicarbonate, tetrasodium pyrophosphate, sodium lauryl sulfate, sodium sacchrinate, hydrated silica, sodium benzoate, citric acid, flavor, potassium carbonate, tea tree oil, sodium monofluorophosphate, thymol and hexylresorcinol.
U.S. Pat. No. 5,041,280 to Smigel, issued Aug. 20, 1991, is directed to a toothpaste containing dicalcium phosphate, calcium carbonate, sodium bicarbonate magnesium carbonate, sorbitol, corn starch, cellulose gum, calcium peroxide, sodium lauryl sulfoacetate, aluminum hydroxide, sodium saccharinate, flavoring, alkylparaben, sodium monofluorophosphate, titanium dioxide and water.
Despite the recent interest in baking soda and peroxide dentifrices, denture creams have not generally adopted baking soda and peroxide. One attractive feature of baking soda and peroxide dentifrices is that they generate bubbles on use, which gives the user a pleasant sensation. This benefit is lost in denture creams, since cleaning is typically done outside the mouth. Also, the generally stronger cleaning agents used in denture creams can adversely affect the baking soda and peroxide. Stability of denture creams containing such ingredients is difficult to achieve.